1. Field of the Invention
The present invention is directed to a method for controlling a fast dynamic scale, particularly suited for fast mixed mail processing in a mail processing system with a dynamic scale and postage-calculating postage meter machine, or with dynamic postage-computing scales and franking devices.
2. Description of the Prior Art
European Application 1 014 050 discloses a method and an arrangement for controlling a dynamic scale that can process mixed mail of different sizes and thicknesses and that can be operated in at least two operating modes, wherein the postal items subsequently pass through a further processing station. The dynamic operating mode is adapted to pieces of mail in a special way, so that there is a high probability of being successfully dynamically weighed. The static operating mode of semi-dynamic weighing begins only after an unsuccessful dynamic weighing.
German Published Application 198 60 295 discloses a method for controlling a dynamic scale, wherein the transport speed of the pieces of mail can be increased in certain operating modes by modifying operating parameters of the dynamic scale. The operating modes are selected by the user via a user interface of a connected postage meter machine. The selection is based on the composition of the stack of letters to be processed. The user knows the composition or can estimate it on the basis of empirical values. However, the advantage of the higher transport speed is lost in the case of an incorrect estimate due to a switching to a reduced transport speed during the dynamic weighing, a re-measurement (if needed) or, given xe2x80x9ctruexe2x80x9d mixed mail, due to the operating mode that has been set. xe2x80x9cMixed mailxe2x80x9d means an unsorted stack of postal items.
According to European Patent 514 107 a control unit interrupts the transport of pieces of mail that cannot be dynamically weighed until the measurement is stable. A detector, that only allows letters to pass for which the weight has been identified, is arranged in the scale close to the downstream end of the conveyor belt. Measurement errors also occur in the semi-dynamic weighing given a non-uniformly distributed mass in the letter and a high transport speed. A stop for the semi-dynamic weighing on the weighing platform couples oscillations into the system again, and this lengthens the measuring time. Such a stop, moreover, can cause the letter to skid from the weighing pan due to its mass moment of inertia. The dimensions of the weighing pan are therefore designed somewhat larger, or the transport speed is set lower, which reduces the throughput given mixed mail.
The maximum clock performance in a dynamic scale is achieved in the non-weighing mode since the transport velocity is increased and the spacing between the pieces of mail can be minimized. In contrast to mixed mail processing, the stack of postal items must be pre-sorted. When this is not assured individual pieces of mail from the stack of postal items can be ejected after a dynamic weighing.
German Published Application 198 58 229 discloses a method for receiving and sorting mail that implements a weight check in relation to the volume of the postal item and rejects inadmissible postal items.
German Published Application 27 17 721 already discloses a system for franking mail shipments having a shunt that is arranged downstream following a dynamic scale. A conveyor device hands the mailing over to the shunt. The mailing is transferred out at the shunt if it exhibits an abnormal weight value. Given a normal weight value, the conveyor device of the shunt conveys the mail items farther to the postage meter machine. A high clock performance of up to 66% of the maximum clock performance is achieved in this way. However, the pieces of mail that have been sorted out are not weighed.
If it is desired that there be no unweighed pieces of mail that have been transferred out, then either an arrangement for semi-dynamic weighing with a stoppage for weighing (U.S. Pat. No. 3,904,946) or a postal matter handling machine with dynamic adaptation of the transport speed for weighing according to the thickness or size of the piece of mail (European Patent 376 481) must be provided. Alternatively, an arrangement for controlling a dynamic scale conveyor system with a dynamic re-weighing (German Utility Model 20001150) can be provided. An adaptation of the transport speed for dynamic weighing or a dynamic re-weighing do not always prove successful. Due to large dimensions (format, thickness) of pieces of mail and, in particular, of pieces of mail having a non-uniform thickness profile, there are pieces of mail for which the prospect of being successfully dynamically weighed is slight. Semi-dynamic weighing comprises a static weighing following an unsuccessful dynamic weighing. The aforementioned times of two weighing operations add to an overall time, i.e., the measuring time for the dynamic weighing, and the time for the stoppage and the static weighing are required in order to obtain a stable measured value.
An object of the present invention is to provide a method for controlling a scale for weighing postal items wherein the weight data can be made available to a further processing station, downstream from the scale in the mail flow, in a more rapid manner than in currently available systems.
The above object is achieved in accordance with the invention in a method wherein the scale is operable in a first mode for dynamic weighing and in a second mode for static weighing, wherein a dimensional characteristic of a postal item to be weighed is determined in a processing station separate from and preceding the scale in the mail flow, with the postal item being conveyed from the processing station to the scale via a transport device, and wherein the scale is automatically set to operate in either the first mode or the second mode dependent on the determined dimensional characteristic.
The invention proceeds on the basis of an early automatic switch in the operating mode. By identifying and evaluating dimensions in a processing station arranged upstream, it is predicted, before the actual weighing event, whether a dynamic or static weighing must be implemented. The times for an unnecessary dynamic weighing and for the transient behavior to subside following the dynamic weighing given a return motion and stoppage are eliminated given dynamic weighing. A shorter transiency for the static weighing and a stoppage of the transport motion occur when the piece of mail moves onto the weighing pan of the dynamic scale. A reverse motion of the piece of mail is not required. The times for a dynamic re-weighing and for a reverse motion are eliminated in the dynamic weighing. A shortening of the overall time is achieved therefrom, and the scale can make the data available to the postage meter machine earlier.
A determination is made in the aforementioned evaluation as to whether the values permitted for a dynamic weighing are exceeded by one of the dimensions or with respect to an allowed thickness profile. An evaluation of the thickness profile of the piece of mail leads to a determination as to whether pieces of mail whose thickness still lies within the range of dynamic weighability could have such an unfavorable weight distribution that results in the expectation of an uncertain weighing result, for example given a position of the center of gravity at the periphery of the piece of mail.